This invention relates to a method for growing photosynthetic microorganisms in liquid suspension, and specifically to the mass culture of unicellular algae.
In recent years cultured algae has been recognized as a promising source of food and even of chemical feedstocks. As a result, a variety of apparatuses and methods have been devised to facilitate the growth of algae. High yields have been obtained in some tightly controlled laboratory experiments, but heretofore, efforts at mass algal culture have been disappointing in that they were inefficient and uneconomical.
Prior mass algal culture systems have yet to prove economical because (1) they require relatively deep containment (20-100 cm) in order to provide for temperature control; (2) they produce comparatively dilute cultures; (3) they make inefficient use of carbon dioxide and little use of infra-red radiations from sunlight; (4) they require substantial energy inputs to provide mixing to avoid thermal stratification; (5) they must process larger volumes of water to obtain the same harvest yields of algal matter that might be collectible from shallower systems; and (6) they permit little or no control and/or regulation of those environmental elements which control and regulate the performance characteristics of the cultured cells.
Further, no prior mass algal culture system has been equipped to induce and regulate the flashing-light effect efficiently. Prior apparatuses have suffered from rapid contamination by unwanted organisms and have required extensive sterilization treatments for both equipment and media. Nutrient and temperature management has not been conducted with precision in such mass culture systems.
Harvesting is usually the single largest deterrent to realizing practical and economical unicellular algal production. The usual methods employed include settling, perhaps enhanced by floculation, centrifugation, and bed evaporation. All such processes require too much time, space, and/or energy to permit reasonable commercial utility.
Even the best of existing apparatus have been operated at less than peak efficiency because currently known methods of operation are not regulated to maximize the production of cell matter.